Goodwill and intangible assets (Schedule of intangible assets subject to amortization) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	$ 98,296
Intangible assets recognized during the period	15,188
Amortization during the period	(5,974)	(16,261)
Currency translation during the period	(2,425)
Intangible assets subject to amortization, ending balance	105,085
Customer Relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	26,210
Intangible assets recognized during the period	0
Amortization during the period	(1,219)
Currency translation during the period	0
Intangible assets subject to amortization, ending balance	24,991
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	71,031
Intangible assets recognized during the period	15,188
Amortization during the period	(4,726)
Currency translation during the period	(2,305)
Intangible assets subject to amortization, ending balance	79,188
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	1,055
Intangible assets recognized during the period	0
Amortization during the period	(29)
Currency translation during the period	(120)
Intangible assets subject to amortization, ending balance	$ 906